Create a seedfile explicitly

Running the entropy unit test creates a suitable seedfile, but this
only works due to the happy accident that no prior unit test needs one
(specifically, test_suite_entropy runs before test_suite_rsa). So
create one explicitly, both for robustness and to keep the script
closer to the version in development where the explicit seedfile
creation is required.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/basic-build-test.sh b/tests/scripts/basic-build-test.sh
index 1862786..1a1a7b9 100755
--- a/tests/scripts/basic-build-test.sh
+++ b/tests/scripts/basic-build-test.sh
@@ -75,6 +75,10 @@
 TEST_OUTPUT=out_${PPID}
 cd tests
 
+if [ ! -f "seedfile" ]; then
+    dd if=/dev/urandom of="seedfile" bs=64 count=1
+fi
+
 # Step 2a - Unit Tests (keep going even if some tests fail)
 perl scripts/run-test-suites.pl -v 2 |tee unit-test-$TEST_OUTPUT
 echo